In optics, optical gratings are used by a number of applications, as they have the property of spectrally spreading incident light by wave-dependent diffraction. Optical gratings can be used, for example, for limiting bandwidth, as well as for tuning wavelength frequency in lasers such as, for example, in dye lasers that can have laser activity in a large frequency range because of the dyes used.
The optical properties of a grating are dependent at least on the number of grating lines and can be further influenced, for example, by the so-called blaze angle of the individual grating steps, coatings, etc. Thus, the gratings used, for example, in a laser resonator, can be optimally selected for the respectively desired application, or the desired frequency range, with which work is to be done in an application, for example, in a laser.
Especially when a high frequency tuning range of a laser system is desired such as, for example, in the case of dye lasers, a range of 500 nanometers, it is known to be a problem that this frequency range cannot be covered by a single grating, as this grating does not have the required unchanging efficiency and sufficient optical properties for the required frequency range. If the same grating were used here for the entire frequency range, this would mean large compromises in the line width or in the efficiency of the laser operation.
In particular, laser resonators that do not work with a simple Littrow configuration of a grating as back reflector but work in grazing incidence using a first grating, the strongest configuration of which uses back reflection with a mirror or a second grating in Littrow configuration by the same grating back into the resonator, have a very small line width, which leads to small-banded resonators.
Such resonators with grazing incidence onto a grating have a so-called Wood anomaly that can lead to a situation in which the laser resonator has an oscillation build-up at certain wavelengths in an undesired polarization.
For this reason, it is necessary in optical apparatuses such as, for example, lasers or also spectrometers that are to be operated in a large, tunable frequency range that more than one grating is used, each of the gratings used being optimized for a respective frequency range.
To achieve this it was previously necessary to change gratings in order to, for example, change from a first to a second or also to additional frequency ranges. This switch was customarily done in that the grating used for wavelength selection is constructed, for example, by the laser resonator or spectrometer or another apparatus in a laborious way and a new grating is installed for the other desired frequency range, after which the optical apparatus had to be recalibrated in order to continue operation.
Solutions also became known in which gratings are arranged on grating carriers that can be fitted to a guide by aligning pins in a predetermined orientation. In spite of that, even with gratings changed in this way, no continuous operation, in particular no laser operation in various frequency ranges can be achieved without subsequent alignment of the gratings.
In addition to the required alignment after such a grating change it must further be considered that frequently, such a grating change is only reluctantly performed by a user and, to do so, a service technician is commissioned in order to do the job that requires time planning, down time of the optical apparatus, for example the laser system, and as a result considerable cost.